In the disclosure of the present invention reference is mostly made to drug delivery devices comprising a threaded piston rod driven by a rotating drive member, such devices being used e.g. in the treatment of diabetes by delivery of insulin, however, this is only an exemplary use of the present invention.
Drug Injection devices have greatly improved the lives of patients who must self-administer drugs and biological agents. Drug Injection devices may take many forms, including simple disposable devices that are little more than an ampoule with an injection means or they may be durable devices adapted to be used with pre-filled cartridges. Regardless of their form and type, they have proven to be great aids in assisting patients to self-administer injectable drugs and biological agents. They also greatly assist care givers in administering injectable medicines to those incapable of performing self-injections.
Performing the necessary insulin injection at the right time and in the right size is essential for managing diabetes, i.e. compliance with the specified insulin regimen is important. In order to make it possible for medical personnel to determine the effectiveness of a prescribed dosage pattern, diabetes patients are encouraged to keep a log of the size and time of each injection. However, such logs are normally kept in handwritten notebooks, from the logged information may not be easily uploaded to a computer for data processing. Furthermore, as only events, which are noted by the patient, are logged, the note book system requires that the patient remembers to log each injection, if the logged information is to have any value in the treatment of the patient's disease. A missing or erroneous record in the log results in a misleading picture of the injection history and thus a misleading basis for the medical personnel's decision making with respect to future medication. Accordingly, it may be desirable to automate the logging of ejection information from medication delivery systems.
Though some injection devices integrate this monitoring/acquisition mechanism into the device itself, e.g. as disclosed in US 2009/0318865, WO 2010/052275 and WO 2010/112575, most devices of today are without it. The most widely used devices are purely mechanical devices either durable or prefilled. The latter devices are to be discarded after being emptied and so inexpensive that it is not cost-effective to build-in electronic data acquisition functionality in the device it-self. Addressing this problem a number of solutions have been proposed which would help a user to generate, collect and distribute data indicative of the use of a given medical device.
For example, WO 2007/107564 describes an electronic “add-on” module adapted to be attached to and measure signals generated by a standard mechanical pen device, the module relying on e.g. the sounds inherently produced by such a device during operation.
Alternatively, in order to provide pre-filled drug delivery devices which more reliably allow detection of an out-dosed amount of drug, it has been proposed to modify such pre-filled drug delivery devices to provide them with structures making them more suitable for cooperation with external detection means, thereby providing more reliable and accurate determination of out-dosed drug amounts. For example, PCT/EP2012/069729 discloses a drug delivery device in which a rotating piston rod is provided with a magnet allowing an add-on logging module to detect the axial position of the magnet by means of 3D magnetometers.
Having regard to the above, it is an object of the present invention to provide components, devices and methods allowing reliable and cost-effective detection of movements generated by a drug delivery expelling mechanism in order to determine amounts of expelled drug.